In the prior art memory device with organic optically sensitive field effect transistor structure, some of the carriers will be stored in between the active layer and the dielectric layer after light illumination; therefore, in order to let carries be stored at the interface stably, the gate voltage needs to be applied so as to maintain memory time, but this will consume additional power. On the contrary, if the gate electrode voltage is not applied, carriers on the interface will combine quickly with the majority carriers in the active layer and get disappeared, hence, the device will lose the memory function and it is thus not suitable to be applied in general portable product.
For example, the optoelectronic memory having optically conductive film as of U.S. Patent No. 20060278866, which uses optically sensitive film as dynamic random access memory, hence, after each signal reading, carrier needs to be supplied.
Nano tube optoelectronic memory device as disclosed in U.S. Pat. No. 5,327,373 uses nano carbon tube as field effect transistor, and then the optical sensitive film is coated on the carbon tube surface. Since nano carbon tube has both the characteristics of metal and semiconductor, hence, according to the current technology, it is still difficult to separate semiconductor and metal nano carbon tube; but if metallic carbon nano tube is used as field effect transistor, the memory characteristic itself will be lost.
In U.S. Pat. No. 6,992,322, optically reactive type organic field effect transistor is disclosed, which uses organic thin film as the field effect transistor; moreover, when different gate electrode voltages are applied, the effects on the response time and memory time to light are discussed. However, the result as disclosed in the embodiment of the patent shows a very short memory time (<60 seconds).